As is conventionally known, the wrist is a very intricate interconnection of several bones, ligaments and tendons. The cooperation of these results in an elegant system allowing for varied and complex movement. FIG. 1 shows the conventional structure, which includes five metacarpals 2, the radius 4, the ulna 6, and eight carpal bones. The carpal bones include the trapezium 10, the trapezoid 12, the capitate 14, the hamate 16, the pisiform 18, the triquetrum 20, the lunate 22, and the scaphoid 24.
As illustrated in FIG. 1, outer surfaces of the scaphoid 24 cooperate with corresponding surfaces of the surrounding carpal bones and the radius.
Arthritis of the wrist is a common ailment. There are multiple etiologies for the development of wrist degenerative arthritis, including trauma, inflammatory, and crystal induced. The two most common causes of wrist degenerative arthritis are scapholunate ligament tears and scaphoid fractures. When a scapholunate ligament tear is left untreated, a progression of degenerative arthritis can occur, known as SLAC wrist. Scaphoid fractures that do not heal and that go onto non-union develop a progression of wrist degenerative arthritis known as SNAC wrist.
In SLAC wrist, the progression of the degenerative arthritis originates at the radial styloid. Due to the abnormal mechanics after a scapholunate ligament tear, the main stabilizer between the scaphoid and lunate is disrupted. As a result, the scaphoid flexes forward and the lunate and triquetrum extend dorsally. Due to the fact that the scaphoid is volar flexed it has difficulty clearing the radial styloid with wrist flexion and extension, causing abnormal wear and degeneration at the radial styloid. This is the first stage of SLAC wrist degenerative arthritis.
The second stage occurs with increased abnormal mechanics at the radioscaphoid joint region. As a result of the scaphoid being in a more flexed position, increased pressure and wear occur on the dorsal aspect of the scaphoid fossa articular surface of the distal radius and dorsal aspect of the scaphoid. With continued abnormal forces and wear, formation of degenerative arthritis occurs. In the third stage, the arthritis occurs at the capitolunate joint, and stage four occurs when the capitate head sinks deeper in the interval between the scaphoid and lunate. In many cases the radiolunate joint is spared, but not always.
In stage 1 of SNAC wrist, the distal pole of the scaphoid cannot clear the radial styloid and degenerative arthritis occurs at the styloid region. In stage 2, degenerative arthritis occurs at the radioscaphoid joint. In stage 3 the arthritis occurs at the capitolunate joint.
In both types, the disease progression is fairly predictable. Conventional attempts at combatting arthritis at any stage generally include reconstructive procedures such as removing carpal bones and/or fusing several of the carpal bones to each other as well as to the radius. These types of drastic procedure can severely limit motion of the wrist after surgery.
Accordingly, there is a need in the art for an improved method and procedure for repairing the wrist.
As a result there is a need for a procedure that can recreate the normal anatomic relationship of the carpal bones, can recreate the normal anatomy and kinematics of the wrist in the earlier stages of the disease, and will lead to improved functional outcomes as compared to the reconstructive procedures that are used presently. To this end, there also is a need in the art for a procedure for replacing the scaphoid while maintaining relative movement of the carpal bones relative to each other as well as relative to the radius and ulna.